OBD-II Code · Sensors
P0142
O2 Sensor Circuit (Bank 1 Sensor 3)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$200–$500
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Some V-engine layouts have a third O2 sensor downstream of the second catalyst on bank 1.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Catalyst efficiency code may follow
Likely causes
- Failed sensorMost common
- Wiring
- Heater element failure
Read the full diagnostic procedureP0142 means the ECM detected a general circuit fault on the bank 1, sensor 3 oxygen sensor — that's the third O2 sensor in the bank 1 exhaust stream,…
P0142 means the ECM detected a general circuit fault on the bank 1, sensor 3 oxygen sensor — that's the third O2 sensor in the bank 1 exhaust stream, which on most vehicles is the post-second-cat (rear-most) sensor used for OBD-II catalyst monitoring and CARB low-emission-vehicle compliance.
The cheapest-first diagnostic ladder
- Visually inspect the harness from the sensor to the ECM connector — sensor 3 lives near the rear of the exhaust where road salt, water, and heat soak chew up the jacketing, and 60%+ of P0142 tickets are a chafed wire or melted connector against the exhaust pipe, not a bad sensor.
- Scan live data for the B1S3 voltage with the engine warm — a healthy narrow-band post-cat sensor should hover steady around 0.6-0.8V with under 0.1V of swing per minute; a reading pegged at 0.45V (bias voltage with no sensor activity), pinned at 0V, or floating randomly between 0.1 and 0.9V is the circuit fault the code is calling out.
- Backprobe the sensor signal and ground wires with a DMM at the ECM connector — you should see continuity under 5 ohms on both, and battery voltage on the heater feed with key on.
- If wiring is good, swap the sensor with a known-good unit ($60-$220 part) and clear codes. The expensive misdiagnosis is replacing the rear catalytic converter on a vehicle with a triple-cat exhaust because the tech assumed P0142 was a catalyst-efficiency code and skipped the wiring check — a $1,800-$3,500 mistake on dual-bank vehicles.
Vehicle-specific patterns2004-2010 Ford F-150 5.4L 3V and 2007-2014 Expedition with the dual-bed (pre-cat + main cat) exhaust on bank 1 sees P0142 from the sensor 3 pigtail m…
- 2004-2010Ford F-150 5.4L 3V and 2007-2014 Expedition with the dual-bed (pre-cat + main cat) exhaust on bank 1 sees P0142 from the sensor 3 pigtail melting against the transmission crossmember after a sagging exhaust hanger lets the pipe drift up.
- 2005-2010Toyota Tundra/Sequoia with the 4.7L 2UZ-FE or 5.7L 3UR-FE V8 throws P0142 from the bank 1 rear sensor connector taking on road spray through a cracked weather seal — the dielectric fails and the signal pin corrodes; a connector repair pigtail clears it for $40 in parts.
- 2003-2008Dodge Ram 5.7L Hemi with NV4500/NV5600 manuals sees P0142 from the rear bank 1 sensor harness rubbing against the bellhousing pivot point.
- 2006-2013Range Rover/Range Rover Sport 5.0L supercharged V8 throws P0142 on bank 1 sensor 3 from heat-damaged harness insulation where the wire runs over the bank 1 exhaust crossover.
Estimated repair$80 to $480.
Look up another code
P0142 — frequently asked
What does a P0142 code mean?
Some V-engine layouts have a third O2 sensor downstream of the second catalyst on bank 1.
What causes a P0142 code?
Common causes: Failed sensor; Wiring; Heater element failure.
What are the symptoms of a P0142 code?
Typical symptoms: Check engine light; Catalyst efficiency code may follow.
Is it safe to drive with a P0142 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $200-$500.
How do I diagnose a P0142 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
More free tools